As both Alx1/Cart1 and Dlx5 mouse mutations result in exencephaly, we hypothesize that changes in expression of these mesenchymal/ectodermal transcription factors may contribute to NTDs associated with Cecr2.

No abstract

The loss of Cecr2, which encodes a chromatin remodeling protein, has been associated with the neural tube defect (NTD) exencephaly and open eyelids in mice. Here, we show that two independent mutations of Cecr2 are also associated with specific inner ear defects. Homozygous mutant 18.5 days post coitus (dpc) fetuses exhibited smaller cochleae as well as rotational defects of sensory cells and extra cell rows in the inner ear reminiscent of planar cell polarity (PCP) mutants. Cecr2 was expressed in the neuroepithelium, head mesenchyme, and the cochlear floor. Although limited genetic interaction for NTDs was seen with Vangl2, a microarray analysis of PCP genes did not reveal a direct connection to this pathway. The mechanism of Cecr2 action in neurogenesis and inner ear development is likely complex.

Although neural tube defects (NTDs) are common in humans, little is known about their multifactorial genetic causes. While most mouse models involve NTDs caused by a single mutated gene, we have previously described a multigenic system involving susceptibility to NTDs. In mice with a mutation in Cecr2, the cranial NTD exencephaly shows strain-specific differences in penetrance, with 74% penetrance in BALB/cCrl and 0% penetrance in FVB/N. Whole genome linkage analysis showed that a region of chromosome 19 was partially responsible for this difference in penetrance. We now reveal by genetic analysis of three subinterval congenic lines that the chromosome 19 region contains more than one modifier gene. Analysis of embryos showed that although a Cecr2 mutation causes wider neural tubes in both strains, FVB/N embryos overcome this abnormality and close. A microarray analysis comparing neurulating female embryos from both strains identified differentially expressed genes within the chromosome 19 region, including Arhgap19, which is expressed at a lower level in BALB/cCrl due to a stop codon specific to that substrain. Modifier genes in this region are of particular interest because a large portion of this region is syntenic to human chromosome 10q25, the site of a human susceptibility locus.